The present invention relates to a printing plate clamping assembly, and, more particularly, to apparatus for clamping flexible thin printing plates in position on a press cylinder. The present invention is primarily directed to an improved arrangement for clamping such thin flexible printing plates in position directly on the press cylinder and on shim members, which shim members are detachably attached to the press cylinder for radially positioning the printing plate with respect to the surface of the press cylinder. Such shim members are utilized in conjunction with existing presses made for earlier used very thick lead stereotype plates. In other words, the shim members serve to account for the difference in thickness between the thin flexible printing plate now generally used and the earlier lead stereotype plates.
New press cylinders dimensioned to fit the new thinner printing plates are substantially more expensive than are spacing members that can be added to existing narrower press cylinders. Therefore, many preferred embodiments of the present invention include shim members and printing plate clamping assemblies usable with such existing narrower press cylinders.
Other preferred embodiments of the present invention are usable with the press cylinders without spacing members. These embodiments include the novel clamping assembly of the present invention in conjunction with press cylinders that are grooved or cutout in accordance with the present invention to accommodate and assist such clamping apparatus. U.S. Pat. No. 3,702,098 to Eburn discloses a known apparatus for utilizing thin flexible printing plates on existing press cyliners. In Eburn specially constructed "saddle members" form the spacer members between the press cylinder surface and the thin printing plates. At the circumferential ends of these saddle members, a special clamping arrangement is provided for engaging and clampingly holding the thin plates on the surface of the saddle members for accommodating printing operations. Although this Eburn arrangement does accommodate for the difference in thickness of the previously used lead stereotype plates and the more practical modernday flexible thin plastic or metal-plastic plates, this arrangement still exhibits the following disadvantages:
1. Because of the required clamping apparatus mounted at the circumferential edge of the saddle member, significant portions of the structural material of the saddle member at such edge portions must be removed. Therefore, the edge portions of the saddle member are substantially weakened. Since the forces experienced in use in printing machines can be very great, especially in the event of a breakdown or paper wrap-up, these edge portions are subjected to frequent breakage, will consequent increased expenses for replacement of the saddler members, not to mention the increased downtime of the printing press to accommodate saddle member changes.
2. The construction of the saddle members, with the required special circumferential end portion cutouts and clamping assembly involves manufacturing complexities.
3. It is desirable to use the same printing machines, with the same press cylinders, for accommodating printing on different widths of paper. For example, due to ecology considerations as well as paper shortages, many newspapers and other publications have changed their page widths as well as column widths to economize on paper usage. With the Eburn arrangement having the clamping assembly built into the shim or saddle members, changes in printing web widths are practically impossible to accommodate without an exchange of saddle members. Web width changes with this arrangement necessarily involve not only the purchasing of different saddle member constructions, but also considerable printing press downtime for accommodating the changes.
4. In printing presses of the type contemplated by the present invention, particularly for accmmodating color printing, it becomes necessary to change the direction of rotation of a given press cylinder during use of the machines. Such change in direction of rotation of the press cylinder requires a reversal in the mounting direction of the thin printing plate. In arrangements such as Eburn, such press cylinder direction reversals generally require removal of the saddle and reversal of same, with respect to the press cylinder. These operations necessarily involve considerable time and expense.
5. In some prior arrangements such as in the Eburn patent, the thin flexible printing plates are placed in position on the saddle members remote from the press cylinder and the assembled configuration is then attached to the press cylinder. These operations require shutdown time for the printing press to accommodate changes, as well as additional personnel and space for accommodating the remote preassembly of the thin printing plates on the saddle members.
The Eburn patent is merely exemplary of various prior art attempts to solve the problem of utilizing the thin flexible printing plates on existing press cylinders. U.S. Pat. No. 3,696,744 to Etchell, U.S. Pat. No. 3,750,572 to Etchell et al., U.S. Pat. No. 3,874,292 to Parsley, and U.S. Pat. No. 3,805,701 to Sonia disclose additional saddle constructions, including clamping assemblies formed at the circumferential edge portions of the saddle members for accommodating attachment of the thin flexible printing plates. The constructions of these just-mentioned patents likewise exhibit substantially all of the above-noted disadvantages of the Eburn constructions. U.S. Pat. No. 3,766,857 to Schlatter also discloses a prior art arrangement requiring special printing saddle lock-up assembly and attachment mechanism at the circumferential edge of the saddle plate members, with the above-noted consequent disadvantages.
Other clamping arrangements for thin flexible printing plates have been disclosed for use with press cylinders, not necessarily requiring separate saddle members or shim means to accommodate for the radial position of the printing plate. However, these other prior arrangments, as exemplified by U.S. Pat. No. 3,552,314 to Skinner et al.; U.S. Pat. No. 3,608,487 to Luehrs; U.S. Pat. No. 3,757,691 to Etchell et al.; and U.S. Pat. No. 3,844,214 to Smith; all require special groove configurations and/or cutouts in the cylinder at the circumferential position of the flexible plate clamp, so that adaptation of these clamps to a saddle-type arrangement would also exhibit the various disadvantages delineated above. Further, these just-mentioned clamps exhibit disadvantages with respect to ease and cost of manufacture, as well as ease and reliability of operation, even when used as suggested on press cylinders without saddle members.
The present invention contemplates the provision of clamping apparatus which avoids the above-noted disadvantages of the prior art arrangements. According to one aspect of a first set of preferred embodiments of the present invention, there is provided a novel arrangement of a clamping assembly and shim members with the shim members being independently and separately attachable to the press cylinder from the clamping assembly. In this manner, the shim members can be constructed without the requirement for any cutouts or grooves to accommodate a clamping assembly, which would otherwise structurally weaken the edge portions thereof. Therefore, the shim members constructed according to the present invention are substantially stronger than the above-noted prior art arrangements with respect to resistance to breakage caused by the substantial build-up of pressure forces at the shim members during printing press malfunctions.
Since the shim members constructed in accordance with the present invention need no cutouts or grooves at the circumferentially facing edge portions, the cost and complexity of producing the shim members is substantially reduced. According to preferred embodiments of the present invention, a simple planar undercut surface at the edge portions of the shim members is provided for accommodating anchoring of the leading edge of the flexible printing plate.
With the clamping assembly per se being formed separately and being attached separately to the press cylinder from the shim members, it no longer becomes necessary to exchange and/or adjust the shim members themselves when changing the clamping assembly and/or adjusting the position of the same.
The present invention also contemplates the inclusion of registration and retaining spring clips with the clamping assembly so as to accurately axially position the leading edge of the printing plate, without requiring any special shim member construction for such purpose.
According to another aspect of the invention, both the shim members and the clamping assembly are constructed in a symmetrical manner so as to accommodate reversal of the circumferential direction of the printing plate without requiring any modifications to the shim member or clamping assembly construction. Since the shim members of preferred embodiments of the invention are constructed with simple planar undercut facing circumferential edge portions, a reversal in the direction of mounting of the thin printing plates is unaffected by the shim member construction.
In preferred embodiments of the invention, a symmetric clamping assembly including a pair of lock bars is provided, each of which lock bars is selectively engageable with the trailing edge of the printing plates to resiliently bias the same into an in-use clamped position. Since the clamping action for the lock bars of this preferred embodiment of the present invention involves only a continuously applied spring force in the clamping direction, exchange and/or reversal of direction of the flexible printing plates merely involves the movement of the respective lock bar to a position enabling engagement of the lock bar with detent means at the trailing edge of the plate, followed by a simple release of the pin bar to perform its clamping function.
In particularly preferred embodiments for use with printing plates having sufficient thickness to exhibit a predetermined rigidity, the detent means at the trailing edge of the plate is a simple smooth bent-over portion without recesses and extending beyond 180.degree. so as to be clampingly engaged by a smooth lock bar.
In other preferred embodiments for use with very thin printing plates, especially pure plastic plates, having less than a predetermined rigidity, the detent means at the trailing edge of the plate includes recesses or apertures formed in a portion of the trailing edge, bent over by approximately 90.degree., which recesses are engaged by pin sections on a lock bar.
According to preferred embodiments of the present invention, the clamping assembly is so constructed as to facilitate removal and exchange of the thin flexible printing plates in a very rapid reliable manner, without requiring any disassembly of the shim members.
The above-mentioned provision of the clamping assembly being completely separate from the shim member construction facilitates changes in web widths of the flexible printing plates, without requiring any changes in the attachment of the shim members. According to another feature of preferred embodiments of the invention, the detent aperture configuration on the printing plates are selected so as to accommodate web width changes without necessarily requiring disassembly and adjustment of the clamping assembly.
In preferred embodiments of the invention, the clamping assembly is mounted so as to be adjustable to accommodate changes in thin flexible printing plates by simple and quick adjustments in the position of the clamping assembly on the press cylinder.
The present invention also contemplates embodiments with a plurality of short clamping assemblies arranged side by side so as to accommodate a multiple-part building block arrangement of the complete clamping assembly, whereby major changes with same can be readily and quickly made. Preferred embodiments of the present invention having the clamping assembly mounted directly to the press cylinder are advantageous in that the same can be very reliably and fixedly mounted at the relatively strong and rigid press cylinder, with the mounting connection thereof having no weakening effects on either the press cylinder or the shim member construction.
Most of the above-mentioned advantages of the clamping assembly of the present invention are also present in preferred embodiments where no shim members are present. In these embodiments, a gap is formed or cutout of the press cylinder to accommodate the clamping assembly. According to preferred embodiments of the present invention the edge portions which face one another to form the gap are formed symmetrically to accommodate simple reversal of the printing plate in a manner similar to the construction of the shim member edge portions discussed elsewhere herein.
Other important features of the present invention relate to the simple reliable compact constructional arrangement of the clamping assembly and the spring clip arrangement apparatus. In preferred embodiments, the clamping assembly is provided with a base member directly attachable to the press cylinder outer surface, which base member directly supports a hinge pin, or hinge pins in a two pin embodiment. The total vertical or radial height of this clamping assembly is maintained very small, while still maintaining the capability of providing high spring clamping forces on the lock bars holding the flexible printing plates in position. The axially extending hinge pins accommodate spiral springs therearound, which springs engage in a very simple manner against the lock bar member to bias the same in the clamping direction with high clamping forces. In the single hinge pin embodiments of the invention, one hinge pin economically accommodates a pair of symmetrically arranged lock bars, which are selectively in use depending upon the mounting circumferential direction of the printing plate.
Other preferred embodiments of the invention have two parallely extending hinge pins spaced from one another. In these embodiments, it is contemplated to accommodate the symmetrical optional reverse direction plate clamping arrangement in instances where the gap between the facing edge of the shim members is too great to accommodate the single pin arrangment. These embodiments are particularly useful for existing cylinder presses and arrangements exhibiting a wide gap between the facing ends of the shim members such as used by some newspapers.
By providing a unitary lock bar, as provided in particularly preferred embodiments, for engagement with the entire width of the flexible printing plate being clamped, it is possible in a simple manner to utilize the manual tool of the present invention to rotate the lock bar for simultaneous engagement of the lock bar along the width of the printing plate to automatically clamp the flexible plate in the assembled in-use position. Likewise, the manual tool can simultaneously disengage the lock bar to accommodate unclamping and removal of the printing plates.
The provision of the recess for the manual tool as spaced from the end of the shim members and press cylinder, preferably in the middle thereof, makes the same readily accessible for plate changes with the recess in the middle of the lock bar resulting in a uniform force when moved.
According to another feature of the invention, the lock bars in the single hinge pin embodiments are dimensioned such that by rotating the lock bars to the respective non-clamping position with the manual tool, ready access to adjustment screws for the axial position (in direction parallel to axis of rotation of the press cylinder) of the base member is obtained.
As also discussed above, the various embodiments of the present invention solve the prior art problems related to press cylinders that require spacer members to radially space the thin flexible printing plates, as well as the prior art problems of press cylinders which support thin flexible printing plates, without such spacer members.
These and further objects, features and advantages of the present invention will become more apparent from the following description, when taken in conjunction with the accompanying drawings and claims.